This family photo shows Madeleine McCann the day she went missing, on May 3, 2007. / AFP/Getty Images

by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

LONDON - British police on Wednesday said they are probing the identity of a serial sex attacker linked to a number of crimes in Portugal as part of the investigation into the 2007 disappearance of Madeleine McCann.

"Officers have identified a potential linked series of twelve crimes which occurred between 2004 and 2010, mostly in low season, whereby a male intruder has gained access to mainly holiday villas occupied by U.K. families on holiday in the Western Algarve," the Metropolitan Police said in a statement.

The man, described by witnesses as having tanned skin with short dark hair, was said to have sexually assaulted five girls aged between seven and ten while they were sleeping in their beds.

"We need to establish the identity of this man," DCI Andy Redwood, the senior investigating officer on the case said, in a statement.

"These offenses are very serious and no one has been charged in connection with them. We also need to eliminate this man from our inquiries and ascertain whether these offenses are linked to Madeleine's disappearance," Redwood said.

Madeleine McCann vanished from the Portuguese vacation resort of Praia da Luz in May 2007, when she was staying there with her parents.

In January, there were reports that police in Portugal were ready to arrest and interview "key suspects" connected to alleged robberies in the area where the then 3-year-old Madeleine was taken in the case that has captivated global attention for years.

However, a former police detective with extensive experience of high-profile investigations told USA TODAY when that lead surfaced that it was being overplayed.

"Burglars don't abduct children," Mark Williams Thomas, who has won awards for his investigative reporting, said. "Child abusers abduct, pedophiles abduct, but if you are in an area burglarizing a house looking for items you are not looking to take a child," he said.

An appeal by British police last year for fresh information generated over 5,000 calls, police said.

"We still need to establish the identity of a man seen by three witnesses, carrying a child fitting Madeleine's description toward the beach or town areas at about 22.00 on the night Madeleine disappeared," Wednesday's statement added, referring to the appeal from Oct., 2013.

"The witnesses have described the man in the e-fits as being white, aged in his 30s, with short brown hair, of medium build, medium height and clean shaven."

Portuguese police officially reopened its investigation into McCann's disappearance around the same time last year.